I'm building a gaming rig for the first time, and I just have a quick question about bottlenecking. How many 5870's in CrossfireX would it take to bottleneck an "perfectly" overclocked i7 920? And by that I mean, overclocked so that the i7 is at an absolute peak performance, without becoming dangerously hot in a non-liquid cooled setup.
It bottlenecks it as soon at you turn it on. EVERY computer is full of bottlenecks, you can not get around them. Something faster is always waiting for something slower. That is what a bottleneck is. Your CPU is full of bottlenecks. Your RAM is a bottleneck for the CPU's L3 cache, which is a bottleneck for the L2, then L1, and so one. Lets not talk about your hard drive, that is probably the slowest thing in your PC besides reading from a CD/DVD. Catching my drift here?
People usually refer to a CPU bottlenecking your video card when it is obvious that there is a huge issue. For example a P4 with a 5850 installed. The example would be if you took out that 5850 and installed a 4850 and got the same FPS. There is obviously such a huge bottleneck that there is no reason to have a higher performing graphics card because the CPU can't process information fast enough to even feet it.
My question to you is why are you asking this question? Do you plan on installing more than 1 5870? if you are planning to install (2) off the bat, why not look at a 5970 instead?